Control of signaling circuits



Nov. 9, 1937. D. MITCHELL CONTROL 0F SIGNALING CIRCUITS Filed July 2. 193s Fl abled at one or more points.

Patented Nov. 9, 1937 CONTROL OF SIGNALING CIRCUITS Deren Mitchell, Bound Brook, N. J., assigner to American Telephone and Telegraph Company, a corporation of New York Application July 2, 1936, Serial No. 88,636

15 Claims.

'Ihis invention relates to electrical signal transmission systems such as telephone systems and, more particularly, to long two-way telephone circuits equipped with wave-responsive devices '-for suppressing singing and echoes With greater particularity the invention is applicable to telephone circuits which are operated antisinging by means of voice-operated devices and include a noisy or otherwise mutable link such as a radio link.

In a long telephone circuit having separate paths for transmission in opposite directions it is oft-en desirable, in order to prevent singing, to have one or both of the one-way paths dis- It follows that means must be provided whereby the voice waves will cause the removal of any such disability normally found on the path over which these waves are to be transmitted. Also, it is usually desirable that the voice waves traveling in one path disable the oppositely directed path in order to prevent the return of echoes.

A telephone system such as that indicated hereinbefore may, however, include what will be l termed hereinafter a mutable Ylink--that is, a

link capable of or liable to change (from internal or external cause) which may give rise to interfering energy, or, more specifically, a link specially subject to noise, fading (in th-e case of `radio transmission) or change of impedance. In such a case the wave-responsive devices on the receiving side of the mutable link, when made sufficiently sensitive to operate on weak speech energy, are liable to false operation by the interfering energy originating in the mutable link.

Various methods of producing satisfactory operation of the wave-responsive devices on thereceiving side of the mutable link have been devised. Examples are disclosed in United States Patents No. 1,674695, issued June 26, 1928 to Nyquist and Wright; No. 1,675,412, issued July 3, 1928 to Holden, and No. 1,999,346, issued April 30, 1935 to Taylor and Mitchell.

It is the principal object of the present invention to provide for the positive operation of theV wave-responsive transmission control devices on the receiving side of the mutable link without considerable overloading of the transmission apparatus associated with that link.

The advantage found in the accomplishment this object and other advantages and featuresv ofY the invention will be understood upon examinaticn of the description contained hereinafter.

In general, the applicant applies to the circuit on the transmitting side of the mutable link, for

transmission over that link simultaneously with the voice or other signal energy, distinctive control energy, which latter energy is adjusted as to magnitude in accordance with variation of the magnitude of the signal energy so that the load applied tol the mutable link is never appreciably greater than the load which would be applied with the transmission of the voice o-r other signal alone. On the receiving side of the mutable link it is provided that the transmission control apparatus will respond positively to the received energy, whether the voice or other signal level be high or low, the received control energy performing the transmission controlling function in the case of low received signal energy.

The following detailed description should be read with reference to the accompanying drawing, of which Figure 1 shows diagrammatically, and in part schematically, a long two-way telephone system including arrangements in accordance with the invention, and Fig. 2 shows in a similar manner, but in somewhat greater detail, a portion of the system disclosed in Fig. 1. Like characters of reference designate corresponding elements and circuit points.

In Fig. l the two-wire circuits C1 and C2 are connected by a long four-wire circuit having the upper path adapted for transmission from left to right and the lower path adapted for transmission from right to left. This extended circuit lying intermediate to the two-wire circuits C1 and C2 comprises the terminal stations S1 and S4 and they control stations. S2 and S3. It will be understood that S1 and S2 and S1 and S3 may be widely separated, but it is con-l templated that the connecting link is quietas distinguished from the mutable link defined hereinbefore. Stations S2 and S3, however, are connected by one or more noisy or otherwise mutable links. It will be understood by those skilled in the art that such a link maybe a radio linkl or some type of wire link, or a combination of radio `and wire links, the characteristic with which the invention is concerned being that which results in interfering energy. 1

The circuit C1 and the oppositely directed paths at station S1 are connected through the usual arrangement of hybrid coil and balancing network, and the circuit C2 and the paths of station S4 are similarly connected.

At each of the stations S1 and S4 there is found a suitable arrangement of wave-responsive transmission control devices which are usually termed collectively .voice operated device anti-singing (vodas). f

At the stations S2 and S3 are located the devices for applying the control current in accordance with the applicants invention and the apparatus for producing the positive'transmission control in response to the energy received from the dis-v The details of the system disclosed in Fig. 11 will be best understood, it is believed, by tracing the operation in response to signal transmission from left to right, for instance, that is, from the circuit C1 to the circuit C2'. The waves divide in the hybrid coil, the useful portion of the energy passing upward and through the one-way amplifier to point a. At this point. a .portion of the energy is diverted to operate an amplifierdetector I which may be termed the vodas amplifier-detector. If there has been no operation of amplifier-detectors responsive to ltransmission in theopposite direction, the operation of ampliiier-detector .I results in the operation of relays Zand 3. 'Relay 2,'in operating, removes from the upper transmission path the disability normally applied'at point o, and thus the voice waves which have been subjected t a'slight delay by:

a suitable circuit are free to pass on over the quiet link to station Sz. The operation of relay 3 disables transmission over the lower path at point z', thus preventing the returnof echo currents and any interference with the transmission from left to right which mightbe produced thereby. q' Y Upon reaching station S2 the transmitted signal energy divides in a hybrid coil 4. Part of this energy passes through a :low-pass Viilter 5 and on to the noisy link, provided-the disability normally applied at point c is removed. The portion of the divided energy passing downward.

from V the hybrid coil Il operates amplier-detectors' and T; Theoutput circuit of amplifier-detector 6 includes the winding of a relay 8 whichV has among its functions thatbfrcmoying, upon operation, the disabilityk at point c and thus clearing the upper path for the transmission of the voice or other signal Waves. The relay 8 may also apply a suppressing disability to'the opposite path at a, point y. Furthermore, this relay, upon operation, removes a short circuit normally applied'between the oscillator I0 and the highpass lter II. Thus, as a result of the operation oi relay 8, there is applied tothe upper transmission path, simultaneously with'the signal energy,Y

control energy iroinjtheoscillator I0, the highpass Vlter i l being included, as shown. This control energy is of aY distinctive frequency which may be termed F1. Associated with the output of amplifier-detectorvl isa device 9 (to .be described in greater detail hereinafter) -which respends to variation ofV theV magnitude of the signalenergy and adjusts the'amountV of control current applied to the circuit from oscillator I0. The variation of themagnitudejof.,the'control current introduced by this device 9; is inverse with respect'to the variation of signal Yenergy magnitude and, as indicated hereinbefore, the adjustment should be such that at no time will thev load applied tothe noisy link be substantially greater than the load which wouldbe applied in the case ofthe signal energy alone. vIn other words, if the signalenergy levelvis high there is applied tothe oscillatorV l0 controlenergyof low magnitude, while if the signal energy is vrelavamplier to the hybrid coil I2.

tively low the control energy applied is of correspondingly greater magnitude.

The hereinbefore described arrangement including the controls exercised by relay 8, permits the application to the signal path and the re- Vmoval therefrom of the control energy Without the introduction of transients of the signal frequencies.

It is to be borne in mind that the voice or other signal waves and the control energy pass simultaneously over the mutable link to station S3.

On the receiving side of the mutable link, unless the upper path has been disabled at point 'J in response to transmission in the lower path, the received energy passes through a one-way The principal part of the energy is to pass the point d, at which there is normally applied a disability. It isthe function of the part of the energy passing downward` from the coil I2 to remove this disability positively. Of the two amplifier-detectors shown, the upper one, I3, is tuned to respond to Voice waves and is set to be comparatively insensitive and thus to operate only in response to comparatively high voice energy. If, then, the received voice energy isV of high level the upper Winding of v relay I5 will be energized and the sin-ging suppressing disability normally applied at point d .will be removed toY permit the passage of the energy from the mutable link. If, on the other hand, the received signal energy is of low level the relay will not operate in response to the output of amplifier-detector I 3.y The band-pass iiiter I4 is designed to pass substantially only the control current, this feature helping to discriminate against noise. The amplifier-detector I5 is thus aiected substantially only by the control current and is designed to operate on all Values of control energy except the lower ones. In other words-this amplifier-detector I5 is adjustedV to operate on the values of control currentcorrespondingto low signal level and not on the values ofcontrol currentV corresponding to the higher signal'levels which will cause the energization of the upper winding of relay I 6. Upon the operation of ampliiier-detector I5 the lower winding of relay I6 is energized and the disability removed from point d. Y

Therelay I6, whether'operated in response to signal or control energy, may have the additional function of applying a Idisability to the f lower-transmission path at point zc.

Y The lter I I in the upper transmission path at station S3 is a low-pass filter designed to pass the .voice'or other signal energy and to suppress the control energy, which has now completed its work. Y

`Upon reaching station S4 the signal energy Voperates the receiving amplier-detector 20,

which may be set to be very'sensitive since noise from the mutable link is present at this point only when signals are coming in. The operation of this amplier-detector 20 disables the output of the transmitting amplifier-detector I and thus prevents false operation at this vodas point in response to echoes. A'I'he control obtained by the operationof amplier-detector I8 and relay I9 at point e, contransmitting amplier-detector at station S4 (I) will cause the operation of relay 3 and disable the upper path at point z. While a portion of the received energy in the upper path is diverted at point f to operate the receiving amplifierdetector 20, the balance of the energy passes on through a delay circuit and a one-way amplifier to the terminal apparatus where the useful portion is applied to the two-wire circuit C2.

The one-way amplifier shown between points e and z permits the operation of relay IB regardless of the condition of relay 3.

It will be understood that transmission from right to left in the circuit specically disclosed is the same with respect to transmission control operations as in the case of transmission from left to right, just described.

As indicated hereinbefore, the complete arrangements of transmission control shown in Fig. 1 serve to suppress cross-transmission if it is present and limit the lockout Zone to the minimum length. Such arrangements are well und erstood in the art, and, apart from their combination with the special control energy arrangements described herein, form no part of the present invention.

In Fig. 2 of the drawing there is disclosed in somewhat greater detail the control energy arrangements associated with the upper transmission path at stations S2 and S3. It will be understood that the control energy arrangements disclosed in Fig. 1, in association with the lower transmission path, may take the form corresponding to that shown in detail in Fig. 2. As has been indicated hereinbefore, voice waves passing the point a: divide in the hybrid coil 4, a part of the energy passing upward and throughr the low-pass filter 5 (upon removal of the disability at point c). 'I'he remaining part of the divided energy passes downward tol operate amplifierdetector 6 and ampliiier-detector II-12. Amplier-detector 6 is set to be very Sensitive and, accordingly, to operate on all values of speech. Therefore, when speech is transmitted relay 8 operates and removes the disability normally applied at point c, and also removes the short circuit normally applied between oscillator IIJ and iilter I I. Such operation permits the application to the transmission circuit of the output of oS- cillator I0, which generates a single-frequency control wave having frequency F1. It is the function of the remaining apparatus disclosed at station S2 in Fig. 2 to vary the magnitude of the control energy applied to the transmission circuit inversely with variation of the magnitude of the transmitted signal energy. Amplier-detector 'II-'I2 is normally adjusted so that there is no current iiowing in the detectory tube 'I2 and, accordingly, no voltage drop across the resistance 92. With this normal condition the push-pull amplifier 93 will have only its normal biasing voltage on the grids, and this voltage is such that a high value of control current will be transmitted from oscillator II) through the highpass lter Il, to be applied to the transmission path when relay 8 operates, but not otherwise.

If the voice waves in amplier-detector 'II-12 represent weak speech, only small current will flow through the 1GO-cycle low-pass filter 9| and there will be only a small voltage drop in resistance 92. Consequently, the control current from oscillator I0 will be applied to the transmission path, for transmission into the noisy link simultaneously with the signals, at practically its full strength. If, on the other hand, the voice waves representstrong speech a comparatively large amount of current will pass through the low-pass iilter 9| and there will b a large voltage drop in resistance 92. Consequently, there will be a considerable addition to the biasing voltage applied to the grids of the push-pull amp-liner 99 and the value of the control current passing through iilter II for application to the transmission path will be low.

The 10D-cycle low-pass filter 9| is included -in the circuit in order to make the control current variation follow the speech envelope rather than the individual waves of speech. This arrangement serves to prevent the excessive modulation of the control waves in the mutable link by the speech and also tends to prevent the control energy from varying over unnecessarily wide ranges of magnitude.

The'operation of the control apparatus shown at station S3 in Fig. 2 has been generally described in connection with Fig. l. Amplierdetector I3 is adjusted to operate only on the higher values of speech energy. Accordingly, this apparatus will not be affected by noise, etc., from the mutable link unless the noise or other interfering energy is so high that it practically renders the circuit useless for commercial transmission. The band-pass filter It designed to pass substantially only the control frequency F1 may be tuned quite sharply. Amplifier-detector I5, as has been indicated hereinbefore, is adjusted to operate on control energy corresponding to the values of speech energy which are too low to produce dependable operation of amplifierdetector, I3. Accordingly, when energy of considerable value is received at station S3 relay IB will operate either on the energization of the upper Winding by speech, or on the energization of the lower winding by the control energy corresponding to the lower values of speech. The operation of relay IS clears the upper transmission path at point d and may also disable the opposite path at point as indicated.

It will be understood that with the applicants arrangement, while the desired operation of the transmission control apparatus on the receiving side of the mutable link ispractically assured, the load applied to the mutable link is never appreciably greater than the load which would be applied by the signal alone. When the voice energy is in the neighborhood of the maximum value the control current may be from 15 to 20 decibels below the signal in magnitude, and the combined eiect of the two types of energy will be only a small fraction of a decibel greater than the eect of the voice alone. On the other hand, if the voice energy is, for example, from lo to 15 decibels below the maximum value, the control energy will approach its maximum value and the total load will exceed by only a small fraction of a decibel the load due to the control energy alone.

While the invention has been disclosed specifically for the purpose of illustration, it is to be understood that it may be embodied in many other and widely different forms without departure from the true invention as dened in the appended claims.

What is claimed is:

1. In a signaling system including a transmitting section, a receiving section and an intermediate link, means associated with the transmitting section and responsive toy signal energy therein for applying distinctive control energy to the system, and means for varying the magnitude of the applied control energy inversely with .variation of the magnitude ofsaid signal energy. 2. In a signaling Asystem including a transmitting section, a receiving section and a mutableintermediate link, means .associatedwiththe transmitting section and responsive tosignal en.- ergy therein for applying distinctive control energy to theV system, means for.varying the magnitude of the' applied control energy inversely with variation of the magnitude of. said signal energy, and transmission control meansA associated with the receiving section and Yresponsive to relatively strong signal energy or, if the signal energy is weak, to the control energy.

3. In a'signaling system including a transmitting section, a normally disabled receiving section and a'mut'ablelintermediate link, the Y method of effecting positive'control of the receiving section which consists' in applying control energy to the transmitting section whenV signal energy is transmitted thereover, causing the4 magnitude of the `applied control energy to vary inversely'with variation of the magnitude of the signal energy, and causing the clearing of the receiving section for transmission thereover to be eiect'ed either by relatively strong signal energy or, if the signal is weak, by the control energy.

4. In a telephone system including a transmitting section, a normally disabled receiving section and a kmutable intermediate link, means Vassociated with the transmitting section and responsive to voice waves therein' for applying to' the system for transmission over said intermediate link simultaneously with the voice waves distinctive control energy'of magnitude inverselyk related to the magnitude kof the voice energy, Yand means associated with the receiving section for clearing the same, said last stated means being responsive to voice Waves of relatively'highl amplitude or, if the amplitude of the voice Waves is low,- tothe control energy.

5. In a signaling circuit designed to be operated anti-singing and including a mutable link, means at the transmitting? end of the mutable link for impressing distinctivecontrol energy on the circuit for transmission over Vsaid link only simulated anti-singing and including a mutable link,

ly with -variationin magnitude of the signal energy,'and means at the receiving end of saidV link for controlling transmission over the circuit, said controlling means being responsive torelativelyhigh signal energy or, if the signalenergy is of low value, to the control energy. n v l l 7. The Ymethod of transmitting control energy over an electrical signal transmission circuitV Without overloading which consists in applying a distinctive wave to the Vcircuit for transmission thereover onlysimultaneously 'witrhthe'signal and causing the amplitudeot said wave to vary inversely with theV strength ofthe signal.

8. In a system for the transmission of electrical Y' signal waves, said systemincluding amutable link and a normally disabled receiving section, the method of controlling transmission without applyingl an excessive. load to the mutable link' which vconsists in impressing a distinctive wave on the system for transmision over said link only simultaneously with the signal, causing the am plitude Voirsaid wave to vary inversely with the.

strength of the signal, and effecting the desired transmission control at the distant end of said link.; including the clearing of the receiving section, in response to the received signal energy if it is` comparatively great and in response to the received control energy if said signal energy is comparatively small.

9.' The method of controlling transmission over a telephone circuit including an Vintermediate mutable link and a normally disabled receiving section, which consists in applyingto the circuit at the transmitting end of saidlink for transmission thereover only simultaneously with the voice distinctive control energy of magnitude varied inversely with variation of the magnitude of the Yvoice energy, and clearing the normally disabled section at the receiving end of said link inresponse either to received voice energy o f relatively high level or to the received control energy if the signal energy level is low.

l0. The method of controlling transmission overaY signaling circuit including an intermediate mutable Vlink and a normally disabled receiving section, which consists in applying to the transmitting end of the mutable link simultaneouslythe transmitted signal energy and distinctive Vcontrolenergyv varying in lmagnitude. inversely withjvariaticn of the magnitude of said signal energy, and producing transmission control at the distant end of said link, including the elearingaof the receiving section, by the combined eiect of the `received signal energy and the received control energy..

11.- In a two-Way signaling system having sep- VaratepathsA for transmitting in opposite directions, eacrh of said paths including two extended Wire sections and an vintermediate mutable link,

' apparatus near each'terminal of the system responsive to transmitted signal energy for preventing singing,-means associated with each path forV transmitting over the mutable link simule taneously with the signal energydistinctive control energy varying in magnitude inversely with variation of the magnitudey of the signal energy, andY means associated with each path near the output from the mutablelink for controlling the` transmission overthe system, said controlling means being responsive to strong received signalsand, if Athesignals are weak, to the received control energy. Y

12. The method `of over a signaling circuit includinga mutable link which consists in transmitting distinctive control energy over. the mutable link only simultaneously with the signalingenergy, and adjusting the magnitude of theV lcontrol energy with relation to variation of the signal' energy so thatvtlie com-r bined magnitude of theenergy of vthe two types is fbelow theloverloadin'g point of the apparatus atY the terminals' of themutable link. I

V13.'The methodY of'controlling transn'lission,V

overa signaling circuit including a mutable link anda normally disabled receiving section, which consists in transmittingrdistinctive control energy Y' over the mutable link only simultaneously with the signal energy, adjusting the magnitude of thecontrol Venergy with relation to variation 'of the signal Venergy so thatvthe combined magnitude of the energy of the two types is below the overloading pointof the apparatus at the tercontrolling transmission minals of the mutable link, and eiecting the desired transmission control on the receiving side of the mutable link, including the clearing of the disabled section, in response to received energy of suiciently high level, whether said energy be predominantly signal or control energy.

14. In a two-way telephone circuit including separate paths for transmission in opposite directions, two terminal stations, two control stations and a mutable link intermediate to the control stations, voice-operated apparatus at each terminal station for suppressing echoes and singing, means at each control station for transmitting over the mutable link simultaneously with the voice waves a control wave of distinctive frequency, said wave varying in amplitude inversely with variation of the amplitude of the voice waves, and means at each control station in association with the receiving side of the mutable link for controlling transmission over the paths at that station in response to voice Waves of sufcient amplitude or,v if the voice energy is loW, in response to the received control energy.

l5. In a two-way telephone circuit including separate paths for transmission in opposite directions, two terminal stations, two control stations and a mutable link intermediate the control stations, voice-operated apparatus at each terminal station for suppressing echoes and singing, means at each control station for transmitting over the mutable link simultaneously with the voice waves a control wave of distinctive frequency, said wave varying in amplitude inversely with variation of the amplitude of the voice waves, and means at each control station in association with the receiving side of the mutable link for controlling transmission over the paths at that station, said last stated means including two amplier-detectors of which one responds to high voice energy and the other to control energy corresponding to low Voice energy.

DOREN MITCHELL. 

